1. Field of the Invention
This invention relates generally to the freeze-drying of formulations comprising a polynucleotide, a block copolymer and a cationic surfactant. In the presence of a cryoprotectant or bulking agent, a formulation can be freeze-dried, whereby upon reconstitution of the dried formulation, the microparticles maintain their optimal size and aggregation or fusion is avoided.
2. Related Art
The use of non-ionic block copolymers as adjuvants in polynucleotide based medicaments has been documented in the art. Polynucleotide complexes which comprise a polynucleotide, a block copolymer and a cationic surfactant have demonstrated enhanced in vivo immune response. In some cases, it is desirable or necessary to supply a suspension of these complexes in a dry powder form that can be reconstituted to an aqueous system just prior to use. One method of drying an aqueous medium is by lyophilization in which the medium is frozen and then the water is extracted by sublimation under vacuum. If the aqueous medium contains a suspension of microparticles, these microparticles tend to cluster during the initial freezing step of the lyophilization process due to the propagation of the crystallization front. Often, the microparticles become permanently aggregated and do not redisperse when reconstituted, creating a population with a very polydisperse size distribution.
Methods for controlling aggregation during freeze-drying and reconstitution through the use of cryoprotectants and bulking agents or other excipients are known in the art and have been described for liposome formulations (See U.S. Pat. No. 5,817,334, hereby incorporated by reference in its entirety), microparticles (See U.S. Pat. No. 6,482,581, hereby incorporated by reference in its entirety) and nucleic acid-polycation compositions (See U.S. Pat. No. 6,251,599, hereby incorporated by reference in its entirety).
Despite these advances, there exists a need for methods by which to freeze-dry and reconstitute compositions comprising a polynucleotide and a block copolymer that also contain a cationic surfactant, such that the same particle size and population polydispersity prior to freeze-drying are maintained following reconstitution. The present invention fulfills this need.